assuming you'd prefer the model to not snap easily in tight turns and stalls i would suggest going for a 12% NACA 0012 at the root and NACA 0018 at the tip (12inch root and 8inch tip)

so the wing is equally thick all the way through.

If you want more root strength than a 12% airfoil can provide then just go for a constant percentage thick wing - e.g. NACA 0015 all the way through.

The spar should be positioned at the thickest point of the airfoil I think its 30% on the NACA 00 series symmetricals.

If you want a tighter turning aircraft you might want to consider a cambered airfoil (non-symmetrical)... I've used Blanchard WB135 recently on a lightweight funfly aircraft and its a gentle stalling, low drag, and reasonably thick airfoil (13.5%). http://www.nasg.com/afdb/show-airfoil-e.phtml?id=1149

i would assume the CG problem is probably related to inadequately small tail area rather than airfoil choice. I suppose if the CG is already far back and you push it even further it could be the straw that breaks the camel's back

An option for a high lift symmetrical could be some of the eppler airfoils designed for full size aerobatic aircraft -

e.g.

eppler 472 http://www.nasg.com/afdb/show-airfoil-e.phtml?id=182
eppler 473 http://www.nasg.com/afdb/show-airfoil-e.phtml?id=183
eppler 474 http://www.nasg.com/afdb/show-airfoil-e.phtml?id=184
eppler 475 http://www.nasg.com/afdb/show-airfoil-e.phtml?id=185
eppler 479 http://www.nasg.com/afdb/show-airfoil-e.phtml?id=186

however i don't know how they'd operate at the low Re's of your 8 inch tip at a flying weight good for a .32 motor.

I've read that they snap easily but can generate a lot of lift but are quite draggy.

hope this helps! good luck and tell us how you get on!